Method of and device for transforming amplitude modulation into phase modulation



March 4, 1952 A gpAzeEK 2,588,302

METHOD OF AND DEVICE FOR TRANSFORMING AMPLITUDE MODULATION INTO PHASE MODULATION Filed April 29, 1949 V FEB TO THE I OSCILLATOR m TO THE MODULATOR myzrivg m. ANTONIN SPACEM BY F 630W Mg-6km Patented Mar. 4, 1952 METHOD OF AND DEVICEiFORTTRANS- FORMING AMPLITUDE MODULATION IN- TO PHASE MODULATION Antonin spaek, Prague-Branik, Czechoslovakia,

assignor of one-half to Tesla, NationalrCorporation, Prague, Czechoslovakia Application April 29, 1949,-Serial No. 90,526 I In Czechoslovakia-May 15, 1948 .6Claims. 1

This invention-relates to a method and device for converting amplitude modulation into phase orafrequency modulationin a simple and efflcientzrmanner.

An :object ofwthe invention is to provide .a method ofrobtaining frequency modulated signalsnby deriving two high frequency voltages of the same. frequency, amplitude modulating lone ofxsuch voltages and .superposing the modulated and .unmodulated voltages to produce .a frequency. modulated output.

Another .object' is .toprovide a method of obtaining frequency modulated signals by deriving two voltages of equal frequency but differing in phase and amplitude, amplitude modulating one of said voltages, and superposing the modulatedand unmodulated voltages.

Still another object of the invention is a device for obtaining frequency modulation in accordance with the above methods.

The. invention will be best understood from the following description to be read in conjunction with the attached drawings in which:

'Fig; 1 shows a circuit forobtaining two voltages having the same frequency, but a certain ratio of amplitudes and phases.

2 "shows the general circuit arrangement of one example or embodiment of theinvention. 'The' physical principle underlying the inven- "tionwill first be explained followed'bya descripa amplitude or a high frequency carrier wave,

aamplitude-modulationdepth given by l the ratio betweenthe amplitude of the modulation "voltage and the amplitude of the voltage of the carrier wave,

"w-2'1rfM, ,fM being the frequency of the modulation voltage, wo--21rfo, f being 'the frequency of the voltage of the carrierwave.

.The fundamental frequenc (1) can be rewrittentas .siiii[( wow) 2 If, in Equation .2 the expression a ,sin (wot-Hp) is substituted for by the. expression The .process thus .mathematically :expressed can be given-various physical embodiments of which one especially simple method will be described. Referringto Fig. 1, a phighirequenoy voltage .'u(t)1is impressed ona pair of input terminals], 2of-a voltage divider circuit having output terminals 2, 3 andi l. The voltage divider comprisestwo sections, each including a,.series connected ohmic resistance and capacitance.

Resistance n of the first section is connected to input terminal I and condenser C1 is,.con

If 01,02. "1-1, .zra arechosen so as tolmeetnthe requirement 3 and if amplitude modulation is carried out for the oscillations (5), then, after superimposing (4) we obtain phase modulation from amplitude modulation.

One practical embodiment of the invention is shown in Fig. 2 in which the divider sections r1C1 and 72C2 are connected in parallel across the secondary of an input transformer having its primary supplied from a stabilized oscillator. The output of r1C1 is applied to one grid of apentode E1, and that of T2C2 is applied to one grid of pentode E2.

The anodes of the two tubes are connected and have a common anode impedance Z which is formed, for example, by a resonant circuit. The bias of the control grid of tube E1 is supplied by battery B1, and the grid bias of tube E2 is supplied by battery B2. The grid bias of the two tubes can, of course, also be obtained by other known means which have not been shown in the drawing being well known to those skilled in the art. Tube E1 acts only as an amplifier or separator, whereas tube E2 also performs another function-namely it provides amplitude modulation. Tubes E1 and E2 must be chosen so that the following conditions should be approximately met.

1. The voltage across the common anode impedance Z must not affect the grid circuits.

2. The mean amplification 9 must be approximately the same for both tubes.

These conditions can be met, for example by using pentodes, and modulation in tube E2 is accomplished by the screen grid which receives the modulation signal from a modulation transformer Tm. The D. C. voltage of the anodes and screen grids of the two tubes is taken from a source which has been shown as battery B2. The primary winding of the modulation transformer TM is connected to the output of a modulation amplifier.

The amplification of tube E1 equals g in this case, and the amplification of tube Ez equals g(1+a. sin wt), where w is 21r-times the modulation frequency supplied to the screen grid of the said tube- The modulation frequency is lower than the carrier frequency and the values of the two frequencies must be kept within known limits acceptable with frequency modulation.

If the above conditions are satisfied, there appears across the anode impedance Z a resulting f voltage If C1, C2, 11, 1'2 are given such values that woC1r1=2 and then, for a sufficiently small :1. Equation 8 represents a phase modulation which is distortionless for practical purposes. This can be easily proved by substituting for 1416) and lied) from Equations 4 and 5 and by comparison with Equations 2 and 3.

Therefore, the system of voltage dividers T101 and T2C2 supplies to the control grid of tube E1 a voltage whose amplitude is /2-times greater than the voltage at the control grid of tube E3 and lagging behind it by of the time duration of one cycle-Le. by 1r, as can be readily proved. Since the working conditions of both that the direct current voltage at the anode Ez' will be amplitude modulated.

The frequency modulated signal produced by superposition of the two voltages across impedance Z can be further amplified or multiplied, as required.

It is, of course, obvious that suitably dimensioned inductances, in the proper sequence, can be employed instead of capacities C1 and C2.

The above described embodiment is, of course, only one example of a great number of possibilities by means of which a frequency modulated signal can be obtained by superposition of an unmodulated signal and an amplitude modulated signal, both signals having the same frequency and the proper amplitude ratio and phase difference, as above mentioned.

We claim:

1. Signalling apparatus, having a frequency modulated output, comprising, in combination a source of potential of fundamental frequency; a pair of voltage divider sections connected in parallel to such source and having relative values such'that the two voltages thus produced are identical in frequency, have an amplitude ratio equal to /2 and the voltage of greater amplitude lags that of lesser amplitude by 31r/4; means for amplitude modulating the voltage of lesser magnitude; and means for superposing the amplitude modulated voltage upon the unmodulated voltage to obtain a frequency modulated output.

2. Signalling apparatus, having a frequency modulated output comprising in combination a source of potential of fundamental frequency; a pair of voltage divider sections connected in parallel to such source and having relative values such that the two voltages thus produced are identical in frequency, have an amplitude ratio equal to /2, and the voltage of greater amplitude lags that of lesser amplitude by 31r/4; means for applying the voltage of greater magnitude to the input of a first grid-controlledelectronic valve; means for applying the voltage of lesser magnitude to the input of a second grid-controlled electronic valve; a source of amplitude modulations; means connecting the last named source to a grid of said second valve; and a common output impedance connected to said valves.

3. Signalling apparatus having a frequency modulated output comprising in combination a source of potential of fundamental frequency; a pair of voltage divider sections connected in parallel to such source and having relative values such that the two voltages thus produced are identical in frequency, have an amplitude ratio equal to /2 and the voltage of greater amplitude lags that of lesser amplitude by 31r/4; means for applying the voltage of greater magnitude to the input of a first grid-controlled electronic valve; means for applying the voltage of lesser magnitude to the input of a second grid-controlled electronic valve; a source of amplitude modulations; means connecting the last named source to a grid of said second valve; and a common output impedance connected to the anodes of said valves.

4. Apparatus as claimed in claim 3 in which each of said divider sections comprises a series connected ohmic resistance and a capacitance.

5. Apparatus as claimed in claim 3 in which each of said divider sections comprises a series ohmic resistance and a capacitance; the ohmic resistance of one section and the capacitance of the other being commonly connected to one terminal of said potential source and the capacitance of such one section and ohmic resistance of the other being commonly connected to the other terminal of the potential source.

6. Apparatus as claimed in claim 3 in which each of said divider sections comprises a series connected ohmic resistance and a capacitance; the ohmic resistance of one section and the capacitance of the other being commonly connected to one terminal of said potential source and the capacitance of such one section and ohmic resistance of the other being commonly connected to the other terminal of the potential source: and the mid junction point of each divider. section being connected to its respective valve input.

ANTONI'N SPAEK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

